The present invention relates to an apparatus for testing soldering states of electronic components mounted on a printed circuit board, and more particularly to a solder testing apparatus for use in a manufacturing process where correct model numbers of electronic components on printed circuit boards cannot be generally identified due to the electronic components having the same electric characteristics being supplied from a plurality of manufactures, or the like.
As for an apparatus for testing soldering states of electronic components mounted on printed circuit boards, there have been failure detecting techniques, for example, as in a high speed solder appearance testing apparatus SV2000 described in Electronic Package Technology, Vol. 9, No. 2, 1993. Specifically, when disturbance occurs, or when a new type of boards are tested for the first time, several boards, appearing to be non-defective, are extracted from a lot and applied to the apparatus to derive a mean value and dispersion from their characterizing amounts, and a failure is determined if the characterizing amounts detected from an object under testing during a test deviate from the mean value of the previously derived characterizing amounts of the non-defective boards by a predetermined amount.
However, the above-mentioned prior art technique has difficulties in supporting disturbance in a process and frequent changes of parts mounted on boards during testing. Generally, even with printed circuit boards under testing of the same type, electronic components labelled with different model numbers, which have the same electric characteristics but possibly slightly different appearances, are often treated as the same components and mounted on the boards. When a plurality of component manufacturers provide electronic components having the same electric characteristics, appearances of the electronic components manufactured by different manufacturers, for example, a lead thickness, a lead width, and so on may slightly differ from each other.
Generally, electronic components used to be mounted on printed circuit boards are supplied from the most beneficial one of manufacturers, which manufacture the components having the same electric characteristics, in terms of the price, delivery time, and so on, at the time the electronic components are to be supplied. For this reason, components from different manufacturers may possibly be mounted on printed circuit boards of the same type depending on manufacturing periods. In the prior art, test data is newly created from non-defective boards only when disturbance occurs in a process during testing. Generally, however, information on used electronic components and changes in processes is not available in a testing step.
For this reason, conventionally, a plurality of components labelled with different model numbers, having electrodes of slightly different design dimensions, have been inevitably subjected to testing using the same image processing parameters and defect determining parameters. Also, while the prior art relies on a mean value for determining a defect, it is difficult for this scheme to conduct a test based on testing specifications used in manufacturing sites. Generally, in manufacturing sites, the testing specifications are generally determined in many cases based on the shapes of leads and pads, for example, a failure is determined when a lead deviates from a pad by three percents or more of the width of the lead. However, since the prior art does not obtain these shapes from images, a highly reliable test cannot be realized.